The formulator of laundry bar and personal cleansing bar compositions is faced with several known problems. Such bars can form various types of gels, especially when stored in-use under circumstances where they can be contacted by water. The bar then softens and smears. Besides being unsightly, this can lead to product wastage. One method of decreasing bar smear is by lowering the water content of the bar. However, bars with reduced water content bars tend to crack on storage. Accordingly, there is a continuing search for new ways to provide improved laundry and personal care bar compositions.
Considerable success in the formulation of soap bars has recently been achieved using the N-alkyl polyhydroxy fatty acid amide surfactants. However, even these superior surfactants do suffer from some drawbacks. For example, their solubility is not as high as might be desired for optimal formulations. At high concentrations in water they can be difficult to handle and pump, so additives must be employed in manufacturing plants to control their viscosity. While quite compatible with anionic surfactants, overall product compatibility can be diminished substantially in the presence of water hardness cations. In addition, there is always the objective to find new surfactants which lower interfacial tensions to an even greater degree than the N-alkyl polyhydroxy fatty acid amides in order to increase cleaning performance.
It has now been determined that the N-alkoxy and N-aryloxy polyhydroxy fatty acid amide surfactants surprisingly differ from their counterpart N-alkyl polyhydroxy fatty acid amide surfactants in several important and unexpected ways which are of considerable benefit to detergent formulators. The alkoxy and aryloxy-substituted polyhydroxy fatty acid amide surfactants herein substantially reduce interfacial tensions, and thus provide for high cleaning performance in detergent compositions, even at low wash temperatures. The surfactants herein are quite compatible with conventional carboxylate soaps as well as with anionic surfactants such as the alkyl benzene sulfates and alkyl sulfates, even in the presence of water hardness cations such as calcium and magnesium ions. This means that the bar compositions herein can be more effective even under the so-called "underbuilt" situation that occurs with many nonphosphate builders. The surfactants herein exhibit enhanced dissolution in water as compared with the corresponding N-alkyl polyhydroxy fatty acid amide surfactants, even at low temperatures (5.degree.-40.degree. C.). The high solubility of the surfactants herein allows them to be formulated as concentrated bars. Moreover, the surfactants herein can be easily prepared as low viscosity, pumpable solutions at concentrations (or melts) as high as 70-100%, which allows them to be easily handled in the manufacturing plant. The surfactants herein also have the advantage of providing a lower sudsing profile than the N-methyl polyhydroxy fatty acid amides, which desirably decreases the carry-over of suds into the rinse bath.
Moreover, the present surfactants, used in combination with conventional anionic surfactants or with conventional soap, provide bar compositions with low smear, appropriate bar hardness with associated decreased wastage, and low tendency to crack on storage.